Data storage on rotating media such as disc drives requires that position information—a servo signal—to be detectable by a sensor. The position information provided in the servo signal allows a head to be accurately positioned with respect to the data storage medium.
On traditional magnetic media, servo information is magnetically encoded on the media. Typically, the servo signal is recorded on the media in a servo-writing process that uses the same systems that write data to the media. The media is typically divided into concentric tracks and sectors. Increased track and sector density permits greater data storage. However, as the number of tracks and data sectors increase, the servo writing process becomes more time consuming.
Magneto-optical systems have also been proposed. With these systems, the servo sector information is written using optical lithographic systems on the surface of a master disc. A series of pits and grooves is formed in this surface, which is then replicated onto the surface of a metal mold. Plastic discs with accurate copies of this pattern may then be produced from the mold by an injection molding processes. Since the servo information is molded into the entire disc surface, writing of individual sector information on the disc is unnecessary. One downside of this system is that increased cost and complexity of the optics system.
In addition, the presence of servo pits and grooves in a media affects the ability of the head to fly uniformly over the recording surface. Variations in fly height can disrupt or distort the servo signal.
A system has been disclosed where servo pits and grooves are filled and the medium is polished to provide a uniform surface that does not disrupt flyability. Systems using this technique are disclosed in U.S. Pat. No. 6,264,848, which is incorporated herein by reference. This process effectively pre-writes the servo information on the disc: The top surface of the disc is divided into servo tracks and data sectors as in a traditional magnetic disc drive, but the servo-writing process is avoided because the servo pattern is fabricated into the disc. Like traditional magnetic disc drives that require servo-writing, this system uses a portion of the disc surface area for providing a servo pattern which reduces the area of the medium available for data storage.
Improved systems for providing servo information are needed.